Travis/Jest: TypeError: Cannot assign to read only property ‘Symbol(Symbol.toStringTag)’ of object ‘#’

That is a bug that came with node v11.11. You can downgrade to v11.10 or wait for the fix which facebook has already pushed (jest error in Node version over 11.11).

If your problem is TravisCI related then you can set a fixed version which works:

node_js:
  - "11.10.1"